ENERGY Flashcards
memorise content
what is power?
power is the rate of energy transfer
unit of power
Watts (W)
Equation for power
P= E/T
Equation for efficiency
Efficiency= useful energy or power output/ total energy or power output (x100) to turn into a percentage
What is efficiency
Efficiency is the proportion/ ratio of TOTAL INPUT energy/power that is converted to USEFUL OUTPUT energy
How is thermal energy usually lost
usually lost from buildings through conduction
INSULATION PRACTICAL STEPS
1) pour hot water into can/beaker, start timer when temperature falls to chosen initial temp
2) after set time, measure final temp
3) repeat with different types of insulation around can/beaker of different layers of the same insulation
Kinetic energy equation
E= 1/2 mv2
Gravitational potential energy equation
E=mgh
Elastic potential energy
E= 1/2 ke2
Thermal energy (SHC) equation
change E= mc change t
ENERGY SOURCES - finite/ non renewable sources
- fossil fuels (coal, oil and natural gas) burned to produce heat, often to produce steam to drive turbines and generators
- nuclear fuel used in nuclear reactions to produce heat
ENERGY SOURCES - renewable sources (can be replaced)
- wind power -wind has kinetic energy, used to turn turbines
-hydroelectric- water behind dam has GPE, falls through turbine - solar power - light from sun produces electricity
SHC PRACTICAL STEPS
1) measure mass of metal block or water in beaker, using top-pan balance
2) place electrical heater in metal block/ water
3) measure initial temp of substance using thermometer
4) turn heater on, start timer and measure p.d and current supplied to heater using voltmeter and ammeter
5) after set time, measure final temp and calculate change in temperature
What is SHC
the energy required to raise the temperature of 1kg of a substance by 1’c
What will happen to the SHC at the end of the experiment?
as energy is lost to surroundings, temp change will be less, so SHC will probably be higher
energy is always ______
conserved
energy cannot be ______________
created or destroyed
What is energy measured in
Joules (J)
ENERGY TRANSFERS
things happen when objects interact (in what we call a system) and energy is transferred from one store to another, or between objects
In a closed system, ________
no energy is transferred from one store to another, or between objects
a system is NOT closed if ____
energy can be lost to the surroundings
SHC PRACTICAL how do you calculate power supplied to the block
P=VI (p.d x current)
SHC PRACTICAL how do you calculate the energy supplied to the block
E=Pt (power x time)
SHC PRACTICAL example apparatus
Joulemeter - measures energy going into the heater in joules (J)
Heater - heats the block
Insulation - stops heating escaping into the atmosphere
Thermometer - measures the temp rise
SHC PRACTICAL why do you need to insulate the block
to stop heat loss to the atmosphere
SHC PRACTICAL why is your answer not the true value
because not all heat was transferred into the block and through to the thermometer
SHC PRACTICAL why is the temperature increase slower at first
because it takes some time for the block to heat up and for the heat to reach the thermometer
What is a system?
A system is an object or group of objects
What happens when a system changes?
When a system changes, there are changes in the way energy is stored. Example a kettle transfers electric energy to thermal energy
What does a Sankey diagram show?
Shows how much of each store or energy there is… it looks like a large rectangle, which splits into arrows. The larger the arrow the more energy stored
How do you gain GPE?
By raising an object above ground level
How is elastic energy stored?
It is stored in a stretched or compressed spring
What is internal energy?
Internal energy is the total kinetic and potential energy of all the particles that make up a system
What does doing work on a system increase?
It increases the energy stored in a system
How does heating change the energy stored in a system?
It increases the energy of the particles within the system
What happens when the energy increases in a system?
Either the temperature will increase or produce a change of state
If the temperature increases in a system, what does the increase depend on?
- the mass of the substance heated
- what the substance is
- the energy input
What is the specific heat capacity?
The amount of energy required to raise the temperature of 1kg of the substance by 1 degree Celsius
What are two key points when looking at energy transfer?
- energy can be transferred usefully, stored or dissipated (spread out to the surroundings)
- energy cannot be created or destroyed
In a closed system, what happens to the total energy?
The total energy never changes, but it can be transferred from one store to another
What is wasted energy caused by?
Unwanted energy transfers
How can unwanted energy transfers be reduced?
- lubrication (reduces the friction that produces heat)
- tightening any loose parts (prevents unwanted vibration that wastes energy as sound)
- thermal insulation (reduces heat loss)
How does a building waste energy?
A building wastes energy when it loses heat to the surroundings, causing it to cool down
What does the rate of cooling through walls depend on?
Depends on the thickness and the thermal conductivity of the walls
What are the main uses for energy resources?
Transport, electricity, generation and heating
What are the 2 different types of energy resources?
Renewable energy resources, which can be replenished
Non-renewable energy resources, which will eventually run out
Examples of renewable energy resources:
Biofuel, wind, water (hydro-electricity), geothermal, tidal, solar and water waves
Main uses of biofuel:
Transport and electricity generation
Key information about Biofuel:
Large areas of land are needed for growing fuel crops. This can be at the expense of food crops in poorer countries
Main uses of Wind:
Electricity generation
Key information for wind:
Does not provide a constant source of energy. Turbines can be noisy/ dangerous to birds. Some people think they ruin the appearance of the countryside.
Main uses of water (hydro-electricity):
Electricity generation
Key information for water (hydro-electricity):
Requires large areas of land to be flooded, altering ecosystems and displacing the people that live there.
Main uses of geothermal:
Electricity generation and heating
Key information for geothermal:
Only available in a limited number of places where hot rocks can be found close to the surface
Main uses of Tidal:
Electricity generation
Key information about Tidal:
Variations in tides affect output. Have a high initial set-up cost. Can alter habitats/ cause problems for shipping
Main uses for solar:
Electricity generation and some heating
Key information for solar:
Depends on light intensity, so no power produced at night. High cost in relation to power output
Main uses of water waves:
Electrical generation
Key information for water waves:
Output depends on waves, so can be unreliable. Can alter habits
Examples of non-renewable energy sources:
Nuclear fuel, coal, oil, gas
Main uses of nuclear fuel:
Electricity generation and some military transport
Key information about nuclear fuel:
Produces radioactive waste but no other emissions. Costly to build and decommission. Reliable output
Main uses for coal:
Electricity generation, heating and some transport
Key information for coal:
Burning produces greenhouse gases (CO2) and contributes to acid rain (SO2). Reliable output
Main uses of oil:
Transport and heating
Key information about oil:
Reliable output. Provides a compact source of energy for transport. Burning produces CO2, NO2 and SO2. Serious environmental damage if split
Main uses of gas:
Electricity generation, heating and some transport
Key information about gas:
Reliable output. Burning produces CO2 but NOT SO2
